The distributed denial-of-service attacks, which also targeted three Israeli banks, were the latest salvo in a month-long offensive between Arab and Jewish hackers determined to give the Middle East conflict an online dimension.

Monday's hacking incident caused the stock exchange's website to perform slowly, while El Al's online services were unavailable for more than an hour.

Responsibility for the attack was claimed by a group of hackers, claiming to be based in Saudi Arabia, which identifies itself by the name "Nightmare".

It came days after a rival Israeli hacking group called "Israel Defenders" published what it said were the credit card details of hundreds of Saudis. Nightmare had carried out a similar stunt after hacking an Israeli sports website.

The self-proclaimed head of Nightmare, who identifies himself as "0xOmar", boasted on the microblogging website Twitter that he would never be caught.

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"No one is this world going to arrest me," he wrote. "It's impossible to find me and I'll keep attacking Israel. Just stay and watch."

Setting himself up against 0xOmar is "0xOmer", the leader of Israel Defenders, who says he is 17. 0xOmer says his counter-campaign has been joined by "7ukk1", allegedly a soldier in Israeli military intelligence. They claim they are poised to release the credit card details of 300,000 more Saudi nationals.

A second Jewish hacker, Hannibal, has joined the fray, publishing details to allow web users to break into the Facebook accounts of 20,000 Arab users. He claims to have the bank account details of 10 million Iranian and Saudi nationals, which he will release if Israel comes under further cyber-attack.

Israeli officials played down the significance of Monday's attacks, saying they had done little damage. Neither El Al nor the stock exchange suffered any disruption to their actual operations, and no sensitive information was stolen.

"Right now, we're not seeing anything that's especially interesting or especially dangerous," Gadi Evron, the former head of internet security for the Israeli government was quoted as saying.

A second security official dismissed the hackers as "teenagers making a noise".